Identification Of Pseudorabies Virus Variant Strain TA-2017 And Genetic Analysis Of Its Major Capsular Glycoproteins

Pseudorabies(PR)is an acute infectious disease that is caused by pseudorabies viruses,which leads great economic loss in swine industry worldwide.The main manifestations of the disease are fever,respiratory symptoms and neurological symptoms,and high morbidity and mortality.At present,the prevention and control of PR mainly rely on vaccination with PRV vaccines madding based on canonical PRV strain such as Bartha-K61.However,since 2011,pseudorabies are happened frequently in vaccine-immunized farms,which were caused by new pseudorabies virus strains that were identified as PRV variant strains.This indicates that the traditional PRV vaccine can no longer provide sufficient protection for the host against infection of variant PRV.Thus,it is quite important to study the characteristics of PRV variant strains and develop new vaccine by use of PRV variant strains.In this study,a pseudorabies virus(named TA-2017)was isolated from a diseased swine farm that was immunized with traditional PRV vaccine in Taian,Shandong Province in 2017.Three major envelope glycoprotein genes including gE,gI and gC were cloned by PCR with the viral DNA of the isolated strain as template.The sequence alignment and genetic evolution analysis of these genes were compared with that of canonical strains and PRV strains isolated after 2011 in China.Sequence alignment showed that the newly isolated strain TA-2017 had the same characteristic mutation site with PRV strains isolated after 2011 in other area of China.Importantly,we found a insertion of aspartic acid(D)at the 48 and 496 sites of gE amino acid sequence,which are typical characteristics of a PRV variant strain,suggesting that the newly isolated TA-2017 is a PRV variant strain that is different from the canonical PRV strains.Phylogenetic analysis showed that the newly isolated strain TA-2017 was located on different branches from the canonical strains,and was located on the same branch of the mutant PRV strains isolated after 2011 in China.In summary,we have successfully isolated and identified a PRV variant strain,which is very useful for further study of new PRV vaccines against PRV variant strain infection.